In modern milking technology, the flow of milk coming from the cow is milked intermittently, and it has added thereto transport air (approx. 8 liters free air per minute) as well as, frequently, major amounts of leakage air. The pulsating two-phase current, which thus occurs in the socalled long milk hose, has to be separated into its two constituent parts milk and air in the milk flow meter and the kinetic energy of this milk flow has to be diminished. In the actual measuring chamber, the milk, which should be degassed to highest possible degree, must flow through the calibrated measuring opening exclusively in accordance with gravitation. It follows that the separated air must be caused to flow past the measuring path via an internal and/or external bypass, without having any opportunity of influencing the discharge behaviour of the milk to be measured.
Furthermore, the cyclic flow fluctation, which is especially caused by pulsation, has to be smoothed as effectively as possible before the milk flows through the actual measuring path of the milk flow meter. In order to eliminate strong surface roughness as well as for minimizing the formation of foam, it will be necessary to diminish turbulences to the best possible extent. Surface roughness and milk foam cause substantial measuring difficulties and impair the signal of the sensor.
For smoothing and degassing the flow of milk, a variety of different means are used often in combination, such as e.g. tangential inflow of the milk into an entrance dome, an entrance cyclone, a deflection shield construction, a prechamber supplying the measuring chamber, if desired, from below, an internal and/or external air bypass etc. The internal air bypass connects the measuring chamber and the discharge chamber and is arranged approximately on the highest level of the measuring chamber. In this case the air will directly sweep over the smoothed and degassed milk, which is to be measured, in the measuring chamber. The dimensions of the bypass must be large enough to provide identical pressure between the measuring chamber and the discharge chamber during the measuring process. An external bypass is used in cases in which the air, after having been separated e.g. in a cyclone, is removed from the cyclone separately and is then introduced in the discharge chamber or in the suction sump only at a point after the measuring path. In the case of this configuration, there is practically no flow of air in the measuring chamber, and this will have a positive effect on the measurement. However, the nature, the structural design and the dimensions of these means will influence not only the function of the milk flow meter but also, directly, the fluctuations and/or losses of the milking vacuum acting on the teat. The milking vacuum, however, must virtually not be influenced by the interconnection of e.g. a milk flow meter for reasons of milking technique and, especially, for reasons of udder health.
In the course of the milking operation, a milk flow profile characteristic of the respective cow is obtained, said milk flow profile varying approx. between 0.2 and, typically, 4 kg/min. Since, however--but this is rarely the case--a milk flow of up to 12 kg/min may be obtained, the flow rate capacity of modern milk flow meters must be adapted to this maximum value. A well-constructed milk flow meter will typically present the following sight: the milk lies comparatively quiet in the measuring chamber and accumulates normally up to a level which is still lower than half the height of the measuring chamber. On top of the milk there is foam of greater or lesser density, which will often extend up to the ceiling of the measuring chamber.
Especially in the case of smaller milk flow meters and in the case of milk fresh from the cow, the formation of such foam on top of the milk can practically never by avoided completely, nor is it possible to avoid milk spray. This means that, when the device is in operation, practically the whole measuring chamber is acted upon by milk components, and these components will then adhere to the measuring chamber and gradually thicken, whereby a hygienically intolerable film of protein and fat would form, if they were not reliably acted upon and removed after each milking operation by an adequate cleaning and disinfecting fluid.
For perfect daily cleaning and disinfection of a milking plant conforming to standard, a flow rate of approx. 2 l/min of rinsing liquid, in connection with a high, fluctuating percentage of air (approx. 40 to 150 l/min), is used in a circulation cleaning process. In view of the fact that the rinsing fluid, too, is smoothed in the interposed milk flow meter, said rinsing fluid will--just as, previously, the milk to be measured--lie in the measuring chamber comparatively quiet and without turbulences and, moreover, it will accumulate up to a level which is lower than one third of the maximum surface level. This means that the upper two thirds of the measuring chamber and the ceiling thereof will practically not be cleaned, and this is absolutely unacceptable for hygienic reasons. In addition, the upper portions of the measuring sensor will not be cleaned either, and, consequently, the use of the normal cleaning method is impossible for functional reasons as well.
Quite generally, it can be said that the better a milk flow meter works and the less its influence on the milking vacuum, the more difficult it is to clean. For carrying out measurements in a milk flow meter, milk and air should be separated as perfectly as possible and all turbulences should be diminished, whereas, for cleaning a milk flow meter, the strongest possible turbulences of a rinsing fluid intensively mixed with air are to be aimed at. An increase of the temperature and/or of the rinsing fluid concentration and/or of the cleaning period are intolerable for economical and/or ecological reasons. The mechanical component (wetting plus turbulence) is the most important factor in the cleaning process of milking machines, and this must also be achieved in the cleaning of a milk flow meter.
Various attempts to solve this problem have already been made. For example, it has already been attempted to simply flood the milk flow meter during the cleaning process by increasing the amount of rinsing liquid. The cleaning result which can be achieved in this way is, in principle, very good. Due to the fact that flooding (overflow) will, however, only take place when the rinsing medium flow rate is higher than the maximum capacity of the milk flow meter (12 l/min), this method necessitates that the flow rate is increased by at least the factor 6 in comparison with the cleaning process normally used for the milking plant. This, however, means that this cleaning process can, at best, be used as an emergency measure, since it stresses economy and ecology intolerably strong by an increased consumption of chemicals, energy and water. Moreover, it is, in practice, frequently impossible to achieve such high flow rates in cases in which the dimensions of other components of the milking plant represent bottle-necks.
An additional solution attempt is the socalled reverse rinsing, i.e. the exchange of the feed hose and of the discharge hose during the circulation cleaning process. This method will cause good turbulences within the whole milk flow meter and, consequently, a thoroughly satisfactory cleaning result. In this case, however, the problem arises that, at the end of the cleaning run, which is controlled by a timing means--since the milker will normally have gone home at this time--the milk flow meter will, due to the exchanged connections, always remain in a condition in which it is filled with rinsing liquid. This is absolutely intolerable for hygienic reasons and in many countries specializing in milk it is even forbidden by law. A vacuum-dependent, automatic drain valve could not successfully be used for final emptying in this case, since such a valve would also respond to short vacuum drops during the milking operation (dropping of the milking means, removal of the milking means) and would thus cause sporadic leakage of milk from the milk flow meter during the milking process. Moreover, at least in large agricultural enterprises, it is, from the point of view of working economy, not tolerable that the feed hose and the discharge hose have to be changed over four times a day in the case of each milk flow meter. In view of the comparatively large inside width (inside diameter 16 mm) as well as in view of the orientation of the hose connecting piece required from the point of view of milking technology, the construction of an adequate airtight two-way cock, which would have a large volume and which would also be difficult to handle, is complicated. Due to the film of grease formed, it would also be problematic to clean the interior of such a cock.
As an additional possibility, it has already been attempted to simply turn the whole milk flow meter upside down. In this case, too, the cleaning effect achieved within the whole interior is, in principle, very good. However, the problem arising in this connection is the same which also arises in the case of the above-mentioned reverse rinsing: the milk flow meter, which is positioned upside down, will not automatically discharge the rinsing liquid at the end of the cleaning cycle. Moreover, in practical everyday use, this type of cleaning can hardly be carried out for reasons of working economy and for ergonomic reasons, since, when the whole milk flow meter is turned upside down, the feed and discharge hoses coupled to the milking means will show a strong tendency to twist, to kink and to become entwined.
Devices for cleaning and disinfecting the milk-flow paths of pipeline milking plants are already generally known from German-pat. 26 08 585, German-Offenlegungsschrift 27 20 987 and German-Offenlegungsschrift 33 45 744.
German-Auslegeschrift 17 57 520 and German-pat. 32 08 197 also disclose devices for cleaning a milk sluice in a milking plant. In the case of such a milk sluice, the milk will normally flow during the milking process from the milk supply conduit via a pre-receptacle into the milk sluice from below. The milk sluice will normally be filled only up to a certain level before the milk will then be discharged from the sluice at normal pressure. Hence, for cleaning also the upper part of the milk sluice with a rinsing liquid, a branch conduit leading from the normal milk supply conduit to the upper end of the milk sluice is provided for the rinsing procedure, said branch conduit containing a valve which is adapted to be opened during said rinsing procedure. However, the use of such an additional conduit, which, during the rinsing procedure, serves to transport the rinsing liquid passed through the milk flow meter instead of the milk to the areas normally not filled with milk, proved to be impossible without a modification of the essential functions of the milk flow meter.